Submitted on: 14 May 1998.
Revised on: 24 June 1998.
Accepted on: 09 August 1998.
___________________Green Materials---EMERALD GROUP PUBLISHING LTD
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Submitted on: 15 May 2014.
Revised on: 29 August 2014.
Accepted on: 16 September 2014.
___________________Green Materials---EMERALD GROUP PUBLISHING LTD
Submitted on: 17 May 2012.
Revised on: 25 July 2012.
Accepted on: 02 September 2012.
___________________Green Materials---EMERALD GROUP PUBLISHING LTD
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Submitted on: 11 August 2004.
Revised on: 17 September 2004.
Accepted on: 08 November 2004.
___________________Green Materials---EMERALD GROUP PUBLISHING LTD